A direct numerical simulation study of the buoyant rise of bubbles at O(100) Reynolds number

Buoyancy-driven motion of bubbles is examined by direct numerical simulations. Two cases, with 48 monodispersed bubbles at two different gas∕liquid combinations, of deformable and nearly spherical bubbles, are simulated. For the nearly spherical bubbles Eo=0.5, and for the deformable ones Eo=4, and for both cases N=8000 and α=5.8%. This results in Re¯=91.5 and We¯=0.53 for the nearly spherical system and Re¯=77.6 and We¯=3 for the deformable one. The simulations show path oscillations of the bubbles in both cases and shape oscillations of the deformable bubbles. At quasi-steady-state, the distribution of the deformable bubbles is relatively uniform but the spherical bubbles are distributed nonuniformly as a result of the formation of horizontal “rafts.” For both cases, however, the probability density functions of the fluctuation velocities of the bubbles are found to be approximately Gaussian. The temporal autocorrelation functions of the fluctuation velocities show that the horizontal components become uncorrelated faster than the vertical component and the correlation time for the vertical autocorrelation for deformable bubbles is at least twice larger than that for nearly spherical ones.